Numerical Electromagnetics Code
Encyclopedia
The Numerical Electromagnetics Code (NEC) is a popular antenna modeling software package for wire and surface antennas
. It is credited to Gerald J. Burke and Andrew J. Poggio, and was originally written in FORTRAN
in the 1970s. The code was made publicly available for general use and has subsequently been distributed for many computer platforms from mainframes to PCs.
solution of the electric field integral equation for thin wires and the magnetic field integral equation for closed, conducting surfaces. The algorithm has no theoretical limit and can be applied to very large arrays or for detailed modeling of very small antenna systems. NEC models can include wires buried in a homogeneous ground, insulated wires and impedance loads.
Models are defined as elements of wire or similar as an input text file (typically in ASCII
). They are then input into the NEC application to generate tabular results. The results can then be input into subsequent 'helper' applications for visual viewing and the generation of other graphical representations as smith charts, etc.
and the University of California
.
NEC-4 currently requires a separate license for use. The licensing details are available from Lawrence Livermore National Laboratory
here.
MININEC was a version first written in BASIC
for home computers. It first emerged in 1982 on the Apple II
computer. MININEC computational engines are
now written in FORTRAN
to improve speed. MININEC is an independent implementation of the method of moments. The basic algorithms are based upon the advice of Professor Wilton at the University of Mississippi (now with the University of Houston).
MININEC suffers from some known flaws compared to NEC, the best known being that resonant frequencies may be slightly in error. However, MININEC handles different wire diameters better than NEC2 and probably NEC4http://www.cebik.com/content/a10/model/fd.html; this includes different diameter parallel wires, different diameter wires joined at an angle, and tapered diameter antenna elements. Placing sources at an intersection of two wires is a problem for NEC2 but not MININEChttp://www.antennamodel.com/mininec.htm. MININEC converges more slowly (requires more segments) when wires join at an angle, when wire segments of significantly different length are adjacent, and has a weaker ground modelhttp://www.antennamodel.com/mininec.htm.
can be simple structures, the modeling of these systems does require a certain level of understanding of the electrical characteristics of antennas.
As a starter for any modeler, 4nec2 or EZnec can be used. See their respective home pages for further information on their purchase and/or installation.
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
. It is credited to Gerald J. Burke and Andrew J. Poggio, and was originally written in FORTRAN
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
in the 1970s. The code was made publicly available for general use and has subsequently been distributed for many computer platforms from mainframes to PCs.
How it works
The code is based on the method of momentsBoundary element method
The boundary element method is a numerical computational method of solving linear partial differential equations which have been formulated as integral equations . It can be applied in many areas of engineering and science including fluid mechanics, acoustics, electromagnetics, and fracture...
solution of the electric field integral equation for thin wires and the magnetic field integral equation for closed, conducting surfaces. The algorithm has no theoretical limit and can be applied to very large arrays or for detailed modeling of very small antenna systems. NEC models can include wires buried in a homogeneous ground, insulated wires and impedance loads.
Models are defined as elements of wire or similar as an input text file (typically in ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
). They are then input into the NEC application to generate tabular results. The results can then be input into subsequent 'helper' applications for visual viewing and the generation of other graphical representations as smith charts, etc.
NEC versions
There are at least four versions of NEC, with NEC-2 emerging in 1981 and NEC-4 appearing in 1992. NEC-2 is the highest version of the code within the public domain without license. NEC-4 remains proprietary with the Lawrence Livermore National LaboratoryLawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
and the University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
.
NEC-4 currently requires a separate license for use. The licensing details are available from Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
here.
MININEC was a version first written in BASIC
BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
for home computers. It first emerged in 1982 on the Apple II
Apple II
The Apple II is an 8-bit home computer, one of the first highly successful mass-produced microcomputer products, designed primarily by Steve Wozniak, manufactured by Apple Computer and introduced in 1977...
computer. MININEC computational engines are
now written in FORTRAN
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
to improve speed. MININEC is an independent implementation of the method of moments. The basic algorithms are based upon the advice of Professor Wilton at the University of Mississippi (now with the University of Houston).
MININEC suffers from some known flaws compared to NEC, the best known being that resonant frequencies may be slightly in error. However, MININEC handles different wire diameters better than NEC2 and probably NEC4http://www.cebik.com/content/a10/model/fd.html; this includes different diameter parallel wires, different diameter wires joined at an angle, and tapered diameter antenna elements. Placing sources at an intersection of two wires is a problem for NEC2 but not MININEChttp://www.antennamodel.com/mininec.htm. MININEC converges more slowly (requires more segments) when wires join at an angle, when wire segments of significantly different length are adjacent, and has a weaker ground modelhttp://www.antennamodel.com/mininec.htm.
NEC in the field
Although antennasAntenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
can be simple structures, the modeling of these systems does require a certain level of understanding of the electrical characteristics of antennas.
As a starter for any modeler, 4nec2 or EZnec can be used. See their respective home pages for further information on their purchase and/or installation.
Limitations
- NEC-2 does not model tapered elements such as those made of telescoping aluminum.
- NEC-2 does not model buried radials or ground stakes.
Public domain resources
- nec2++ - A GPL port of NEC-2 to C++, with a C/C++ interface and python bindings. It can easily be incorporated into automatic optimizers.
- 4nec2 - A free NEC2/NEC4 implementation for Microsoft WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
. It is a tool for designing 2D and 3D antennas and modeling their near-field/far-fieldNear and far fieldThe near field and far field and the transition zone are regions of the electromagnetic radiation field that emanates from a transmitting antenna, or as a result of radiation scattering off an object...
radiation patterns. - L. B. Cebik's Antennas, Service and Education - A great repository of antenna modeling and related information, particularly including the survey Some Antenna Modeling Programs.
- Numerical Electromagnetics Code NEC2 unofficial home page - NEC2 documentation and code examples
- MMANA - A free antenna modeling program based on MININEC.
- Xnec2c - A translation of NEC2 into C, NEC2C, and a GTK2 based GUI, Xnec2c.
- NEC Lab - NEC Lab is a powerful tool that uses Numerical Electromagnetics Code (NEC2) and Artificial Intelligence (AI) to design antennas.
- CocoaNEC - Open source GUI front-end for Apple OS X. Includes NEC2 and supports NEC4 with separate license.
Commercial resources
- EZnec - A well known commercial-based antenna modeling package based on NEC3 and NEC4.
- NEC4WIN NEC4WIN /VM - A Windows XP, Vista simulation program based on Mininec 3.
- AC6LA antenna utilities - A collection of commercial antenna utilities
- Nec-Win plus - A commercial modeling package.
- GAL-ANA - A commercial antenna modeling package based on NEC2 and MININEC.
- GNEC - A commercial NEC package with a graphical user interface.